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High-performance Materials History Part 5 - Composites


Big performance gains are already well in hand for the class of materials called composites in which one type of material is reinforced by particles, fibers, or plates of another type. Among the first engineered composites was fiberglass, developed in the 1930s. Made by embedding glass fibers in a polymer matrix, it found use in building panels, bathtubs, boat hulls, and other marine products. Since then, many metals, polymers, and ceramics have been exploited as both matrix and reinforcement. In the 1960s, for instance, the U.S. Air Force began seeking a material that would be superior to aluminum for some aircraft parts. Boron had the desired qualities of lightness and strength, but it wasn't easily formed. The solution was to turn it into a fiber that was run through strips of epoxy tape; when laid in a mold and subjected to heat and pressure, the strips yielded strong, lightweight solids—a tail section for the F-14 fighter jet, for one. While an elegant solution, boron fibers were too expensive to find wide use, highlighting the critical interplay between cost and performance that drives materials applications.

Many composites are strengthened by graphite fibers. They may be embedded in a matrix of graphite to produce a highly heat-resistant material—the lining for aircraft brakes, for example—or the matrix can be an epoxy, as with composite shafts for golf clubs or frames for tennis rackets. Other sorts of composites abound in the sports world. Skis can be reinforced with Kevlar fibers; the handlebars of some lightweight racing bikes are made of aluminum reinforced with aluminum oxide particles. Ceramic-matrix composites find use in a variety of hostile environments, ranging from outer space to the innards of an automobile engine.

Tens of thousands of materials are now available for various engineering purposes, and new ones are constantly being created. Sometimes the effort is grandly scaled—measured in vast tonnages of a metal or polymer, for instance—but many a recent triumph is rooted in exquisite precision and control. This is especially the case in the amazing realm of electronics, built on combinations of metals, semiconductors, and oxides in miniaturized geometries—the fingernail-sized microchips of computers or CD players, the tiny lasers and threadlike optical fibers of communications networks, the magnetic particles dispersed on discs and other surfaces to record digital data. Making transistors, for example, begins with the growing of flawless crystals of silicon, since the electrical properties of the semiconductor are sensitive to minuscule amounts of impurities (in some cases, just one atom in a million or less) and to tiny imperfections in their crystalline structure. Similarly, optical fibers are composed of silica glass so pure that if the Pacific Ocean were made of the same material, an observer on the surface would have no difficulty seeing details on the bottom miles below. Such stuff is transforming our lives as dramatically as steel once did, and engineering at the molecular level of matter promises much more of the same.


     High-performance Materials
     More Synthetic Polymers
     Essay - Mary L. Good

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